Another option: Use a MonoNote to trigger the sample -- and possibly also load the loop into the SamplePlayer instead of the DrumKit. The SamplePlayer has a larger wave display, which makes it easier to tweak loop points (if you need to). For the MonoNote Pattern, either setup a step that is 1 bar long with at 95% gate, or use a shorter subdivision (say 1/16 notes) where all steps but the last one are tied. The advantage of the MonoNote here vs. the DrumSeq is that you can tweak that one loop w/o messing up other parts.

If you need to adjust the loop speed to match tempo, use the pitch adjust in the SamplerPlayer (or DrumKit) to get it to match, then, if you want, use an AUPitch plugin to adjust it back to the pitch you want. It won't sound like the original if you tweak more than a semitone, but sometimes that's what you'll want...